1. Field of the Invention
The present invention relates generally to apparatus and methods for transporting and metering particulate material. More particularly, embodiments of the present invention are directed to a particulate material handling device which can be used to both transport and meter solid material of a great range of sizes under both ambient conditions and against pressure.
2. Description of Related Art
A wide variety of equipment has been used to either transport or meter particulate material. Such transport equipment includes conveyor belts, rotary valves, lock hoppers, screw-type feeders, etc. Exemplary measurement or metering devices include weigh belts, volumetric hoppers and the like. In order to provide both transport and metering of particulate material, it has generally been necessary to combine or incorporate both types of devices into a system.
One or more of the above identified transport or metering devices may be used in a solids transport system, depending upon a wide variety of parameters. For example, the amount, size and type of particulate material to be transported must be taken into consideration. The distance over which the solids are to be transported and variations in the surrounding pressure during transport must also be taken into account. The various transport and metering systems which are presently in use all have a variety of advantages and disadvantages which limit their performance in transporting or metering a wide variety of particulate types. It would be desirable to provide a single unit which is capable of simultaneously transporting and metering a wide variety of particulate materials under both ambient and pressurized conditions.
Large scale transport and/or metering of coal presents unique problems. A transport apparatus or system which is suitable for transporting one type of coal may not be suitable for transporting a different type of coal. For example, Kentucky coals maintain reasonable integrity when transported through conventional devices such as screw feeders and conveyor belts. However, Western United States coals tend to be more friable and may be degraded to a significant degree during normal transfer operations. It would be desirable to provide an apparatus which is capable of transferring all types of coal with a minimum amount of degradation.
The water content of the particulate solids is another factor which must be considered when designing any transport system. Many transport devices which are suitable for transporting completely dry particles do not function properly when the moisture content of the particulate material is raised. The same is true for particulate metering devices. Conventional metering devices which are designed to measure dry particulates are not well suited to meter moist solids. It would be desirable to provide a transport apparatus which is capable of moving and/or metering particulate solids regardless of their moisture content.
There are also many instances in which it is desirable to transport and meter particulate materials against pressure (e.g., wherein the pressure of the atmosphere and/or of fluids or solids at the output side of the transport system is greater than the pressure at the input side of the system). It would be desirable to provide an apparatus which is capable of simultaneously pumping and metering under both ambient pressure conditions and against a pressure head caused either by entry into a pressurized system or transport of the particulate material upward against gravity.
It is apparent from the above background that there is a present need for a solids handling or pumping device which operates as a single unit to provide simultaneous transport and metering of particulate material. The unit should be capable of transporting and metering a wide variety of particle types under a wide variety of conditions. Further, the unit should be structurally strong, and mechanically simple and durable so that it can be operated continuously over extended periods of time without failure.